Hard disk drives, which are widely used as a data storage device for computers and like devices, include a magnetic head for reading user data stored on a magnetic disk or writing user data onto a magnetic disk. The magnetic head is mounted on an actuator that is oscillated by a VCM (voice coil motor). When the magnetic head reads or writes user data, the actuator is driven to move the magnetic head to a specific track (target track) for positioning purposes. Magnetic head positioning control is exercised in accordance with servo information stored on a magnetic disk to move the magnetic head to a specified position. In line with recording density improvement, hard disk drives released in recent years have begun to use an MR (magnetoresistive) head, GMR (giant magnetoresistive) head, or other magnetoresistive device, which produces a magnetoresistive effect, as a read-only read head, and a transducer induction head as a write-only write head. These two heads, which constitute a composite magnetic head, are mounted on the same support called a slider, but positioned at a predetermined distance from each other. The slider is mounted on the actuator.
A plurality of data tracks are concentrically formed on a hard disk or other magnetic disk. Further, servo tracks, which store identification information and burst patterns beforehand, are formed in the radial direction of a magnetic disk. The aforementioned servo information comprises the identification information and burst patterns. The identification information indicates the track address of a data track. The identification information acquired by the read head is used to determine the data track on which the read head or write head is positioned. As the burst patterns, a plurality of burst pattern rows, which differ in signal storage area phase, are employed so that various signal storage areas are arranged at fixed spacing intervals and in the radial direction of a magnetic disk. In accordance with a signal (PES: position error signal) that is generated by the read head depending on the burst patterns, the deviation of the read head or write head from the target data track can be detected.
The servo information is written onto a magnetic disk in a manufacturing process that is performed prior to hard disk drive shipment as a product. For an accurate read/write of user data, the servo information, which serves as the reference, needs to be accurately written. Conventionally, a dedicated device called an STW (servo track writer) was used to write servo information onto a magnetic disk. The STW writes servo information onto a magnetic disk while controlling the feed pitch (write position in the radial direction of a magnetic disk) of a magnetic head (write head) for writing servo data at a track pitch (distance between the centers of adjacent tracks) and the timing with which servo information is to be written (write position in the circumferential direction of a magnetic disk). A known method for setting the magnetic head's feed pitch is to determine the absolute position of the magnetic head (write head) by pressing a push pin against the actuator on which the magnetic head is mounted. A known method for setting the servo data write timing is to write clock data onto the outer area of the magnetic disk by using a dedicated clock head and use the written clock data as the reference clock.
However, the use of the above methods makes it necessary to write clock data onto a magnetic disk with the clock head or press the push pin against the actuator. It means that the hard disk drive needs to be uncovered for a servo information write. Therefore, the use of the above methods imposes a restriction that the servo information write must be performed within a clean room.
Under these circumstances, the inventors of the present invention proposed a method for performing a servo information self-write without using the aforementioned clock head or push pin (refer to Patent Document 1). This proposed method makes it possible to write servo information onto a magnetic disk outside a clean room and without having to uncover the hard disk drive.
[Patent Document 1]
Japanese Patent Laid Open No. 2002-8331
For servo information write purposes, the self servo write method disclosed by Patent Document 1 writes a special servo pattern, which is called a propagation pattern, onto a data track in addition to servo information, and reads such a propagation pattern to exercise servo control.
However, propagation-pattern-based servo control differs from common servo control for a hard disk drive. Processing required for propagation-pattern-based servo control cannot be completed by using a hard disk controller (HDC) and MPU (microprocessing unit) built in a hard disk drive as well as software. In general, it is necessary to connect an STW that is dedicated to a self servo write and provided with a powerful processor and software.